1. Field of the Invention
The present invention relates to a means in a motor-driven rail-vehicle, comprising a drive wheel driven by a drive motor.
2. The Prior Art
FIG. 1 shows how in a rail-vehicle, the tractive force F varies with the difference .DELTA.v between the peripheral speed of the drive wheel and the speed of the vehicle. To a relatively great extent the appearance of the curve depends on the surface of the rails and drive wheels, the existence of contamination, rust, ice, etc., and the speed of the vehicle. In principle, however, when the tractive force increases from zero up to a certain value F.sub.1 then .DELTA.v increases, due to elastic deformations, relatively slowly up to a certain value .DELTA.v.sub.1. In a typical case F.sub.1 is about 75 % of F.sub.max. If the tractive force increases further, pronounced slipping occurs between wheels and rail. Maximum tractive force F.sub.max is obtained when .DELTA.v = .DELTA.v.sub.2. .DELTA.v.sub.2 is normally one or a few km/hour. If .DELTA.v increases further, the tractive force decreases.
It is extremely desirable to be able to exploit the maximum available tractive force when necessary, i.e. to be able to work in a stable manner with .DELTA.v = .DELTA.v.sub.2, where of course F = F.sub.max. Since as mentioned above, the appearance of the curve, and thus both .DELTA.v.sub.2 and F.sub.max, vary relatively strongly with uncontrollable external conditions, it has so far been impossible to fulfil this desire. The invention now shows a means with the help of which this problem is solved in a simple and advantageous manner.